1. Field of Invention
The present invention relates to an image display apparatus having a metal outer housing. More particularly, the invention relates to an image display apparatus that can be used for a projection display apparatus having a metal outer housing for housing components such as a light source lamp, a modulation device for modulating light emitted from the light source lamp according to image information, and a projection lens for performing zoom-in projection of modulated light onto a projection screen.
2. Description of Related Art
Recent personal computers are small and light. Image display apparatuses for such personal computers, such as displays and projection display apparatuses to be used with such electric equipment, are also required to be proportionally smaller and lighter.
In making such small and light image display apparatuses, considerations described hereinbelow are necessary. A material for an outer housing of the image display apparatus must be one in which the wall thickness of the outer housing can be as small as possible while the strength of the outer housing of which the wall thickness is small must be sufficiently high. Furthermore, in proportion to the size reduction of the image display apparatus, the structural density of components in the apparatus is greater. Therefore, for prevention of heat accumulation, it is preferable that a highly-radiative material be used for the outer housing. Furthermore, since various circuit substrates are included in the image display apparatus, a material applied with an EMI (electromagnetic interference) countermeasure must be used for the outer housing. Furthermore, from the viewpoint of resource-conservation and resource-recycling recently demanded for such electronic apparatuses, the outer housing is preferably formed of a monometallic material that can be easily recycled as a resource, not a material such as a synthetic resin or a metal hybrid material.
Recently, in order to meet the aforementioned requirements for smaller and lighter outer housings, outer housings formed of metal such as a magnesium alloy have been proposed.
As a method for integrally forming such metal outer housings, a thixotropic forming method is known in addition to methods such as casting and forging. In this method, a semimolten metal slurry in both solid and liquid phases is stirred so as to reduce viscosity for carrying out injection-molding.
Compared to a casting method, such as a die-casting method, the thixotropic forming method has more advantages. One of the advantages is that since injection materials can be formed at a lower temperature, less shrinkage occurs due to coolcaking, allowing higher dimensional precision to be obtained. Another advantage is that since surfaces of formed articles are denser, processings such as buffing to be performed after molding, can be simplified.
Nevertheless, the thixotropic forming method still causes problems in injection molding outer housings such as those described above. In the forming process, the semimolten metal slurry is injected at a lower viscosity in a stirred state, its viscosity gradually increases in the mold, causing solidification during filling. Therefore, in this method, filling the semimolten metal slurry into the mold in the shortest possible time is a problem to be solved. Particularly, significant problems arise regarding reduction in filling time for forming a large outer housing and improvement of filling characteristics so as to obtain improved appearance and precision in the formed housing in a case where the molten metal flows at a high speed.
It is therefore an object of the present invention to provide an image display apparatus having a metal outer housing that will allow improved filling characteristics so that the thixotropic forming method can be performed in shorter time.
To achieve the aforementioned objects, the present invention is characterized in that improvement considerations and ideas are introduced with respect to the structural shape of the outer housing so that the semimolten metal can be filled out in individual molds in the thixotropic forming method in shorter time.
Particularly, according to one aspect of the present invention, there is provided an image display apparatus having an outer housing formed of metal in a thixotropic forming method, in which the outer housing includes a reference surface formed along a direction in which semimolten metal flows in forming processing, and an step surface formed so as to face toward a downstream side of the foregoing semimolten-metal flow direction and so as to intersect with the reference surface, the foregoing step surface comprising a bevel section beveled down at least on a part thereof in the foregoing semimolten-metal flow direction.
In this case, the bevel section may be formed substantially to guide the flow of the semimolten metals, therefore, it may be beveled down along the semimolten-metal flow direction, or it may be beveled down so as to diagonally intersect with the semimolten-metal flow direction. The beveled section may be also formed of a certain slant surface shape or a curved surface shape in which the gradient varies depending on the positions. Furthermore, the bevel section may be formed entirely on the step surface, or it may be formed by bevel-cutting a section where the reference surface and the elevated section intersect each other.
According to such an invention in which the bevel section is formed on the step surface, when the semimolten metal arrives at an intersection of the reference surface and the step surface, it is guided by the bevel section so as to quickly flow through the step surface. This reduces filling time of the semi-molten metal into molds in the thixotropic forming method when forming the outer housing.
According to another aspect of the present invention, there is provided an image display apparatus having an outer housing formed of metal in a thixotropic forming method, in which the outer housing includes a reference surface formed along a direction in which semimolten metal flows in forming processing, the foregoing reference surface having convex sections extending in the direction in which the semimolten metal flows.
According to such an invention, since the convex sections are formed on the reference surface, the semimolten metal quickly flows along the convex sections, allowing time for filling the semimolten metal to individual molds to be reduced. This arrangement is particularly effective for forming a large and thin-wall housing such as an outer housing of a projection display apparatus.
In this case, it is preferable that the reference surface have a supporting rib formed so as to intersect with the convex sections and so as to protrude from the reference surface. In such an arrangement in which the supporting rib intersecting with the convex sections is formed, the semimolten metal flowing on the convex sections diffuses at an intersection with the supporting rib, by which time for filling the semimolten metal can be further reduced.
When the reference surface has openings, it is preferable that the supporting rib be formed along internal peripheries of the openings. In more detail, when a plurality of openings are orderly arranged along the flowing direction, it is preferable that the supporting rib is arranged along borders dividing the openings adjacent to each other.
Since the supporting rib is formed along the internal periphery of the opening of the reference surface, time for filling the semimolten metal into a periphery of the opening can be reduced. In addition, the opening periphery is to be reinforced by the supporting rib after forming, by which the strength of the outer housing can be increased. Such an arrangement is notably advantageous in terms of reduction in filling time of the semimolten metal and reinforcement efficiency by the supporting rib particularly when a plurality of openings is formed in order in the semimolten metal flow direction, as described above.
Furthermore, in such an outer housing, when a peripheral frame is formed so as to surround the reference surface and so as to have a thickness greater than the thickness of the reference surface, the supporting rib is arranged preferably so as to connect with the foregoing peripheral frame.
When the peripheral frame is formed so as to have the wall thickness greater than that of the reference surface of the outer housing, the strength of the outer housing after forming can be greatly increased. Furthermore, in this case, since the peripheral frame and the supporting rib are arranged to connect with each other the semimolten metal can be filled so as to flow therethrough quickly, allowing reduction in filling time and improvement in appearance of the formed housing.
According to another aspect of the present invention, there is provided an image display apparatus having an outer housing formed of metal in a thixotropic forming method, in which the outer housing includes a reference surface formed along a direction in which semimolten metal flows during the forming processing. The protrusions are formed so as to protrude from the reference surface, the protrusions comprising flowing ribs at inflow sides thereof for guiding the semimolten metal thereinto. The protruded flowing ribs may be formed either in a triangular having a straight edge or in a form having a radial edge.
According to such an invention in which protruded flowing ribs are formed on the inflow side of the protrusion, the semimolten metal is allowed to flow quickly into the protruding sections through the flowing ribs, by which filling time can be reduced.
Furthermore, the thickness of a section of the reference surface is preferably 3.0 mm or less, or more preferably 1.5 mm or less.
In a trend in which image display apparatuses are required to be lighter, although the magnesium alloy is used as a material for the outer housing, the weight of the outer housing must be less than that of a synthetic resin outer housing. From this point of view, the thickness of the reference surface of the outer housing must be predetermined to be 3.0 mm or less, preferably 1.5 mm or less, so as to be equal to or less than a specific-gravity ratio of the magnesium alloy and the synthetic resin material (about 0.6 to 0.7). To form a large outer housing having a wall thickness of 3.0 mm or less, flowing and filling time of the semimolten metal are problems. However, use of the present invention allows a significant reduction in filling time, and in addition, enhancement of appearance and precision in the housing formed in the thixotropic forming method by improving the filling characteristics.
According to another aspect of present invention, there is provided an image display apparatus having an outer housing formed of metal in a thixotropic forming method, in which the outer housing includes an upper housing for covering an upper surface of the apparatus, a lower housing for forming the bottom face of the apparatus, side housings arranged between the foregoing two housings for covering side faces of the apparatus, a rear housing for covering a rear face of the apparatus, and a front housing for covering a front face of the apparatus, the foregoing upper housing, lower housing, side housings, rear housing, and front housing being formed as plates and being independently formed.
According to such an invention in which the individual housings such as the upper housing composing the outer housings are formed as plates and are independently formed, the semimolten metal flows smoothly and filling time can be reduced.
According to another aspect of the present invention, there is provided an image display apparatus having an outer housing formed of metal in a thixotropic forming method, in which the outer housing includes an upper housing for covering an upper surface of the apparatus, a lower housing for covering the bottom face of the apparatus, side housings arranged between the foregoing two housings for covering side faces, a rear housing for covering a rear face of the apparatus, and a front housing for covering a front face of the apparatus. In the above, the upper housing and the lower housing are individually formed such that they are bent along edge lines on the side of the side housings by a predetermined width in the directions opposing each other, and the upper housing, the lower housing, the side housings, the rear housing, and the front housing are independently formed.
According to such an invention in which the upper housing and the lower housing are bent by a predetermined width in the directions opposing each other and are nevertheless substantially in the form of a plate, and other housings are arranged individually in the form of a plate and are formed independently, the semimolten metal flows smoothly and filling time can be reduced.